Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$194.86	12.689%	$219.5858	$219.59	$219.60	$219.60
Purchase #2	$137.69	11.561%	$153.6083	$153.61	$153.60	$153.60
Purchase #3	$41.47	5.758%	$43.8578	$43.86	$43.85	$43.90
Purchase #4	$196.71	4.279%	$205.1272	$205.13	$205.15	$205.10
Purchase #5	$212.44	12.812%	$239.6578	$239.66	$239.65	$239.70
Purchase #6	$16.71	11.437%	$18.6211	$18.62	$18.60	$18.60
Purchase #7	$25.43	13.743%	$28.9248	$28.92	$28.90	$28.90
7 purchase totals =	$825.31		$909.3828	$909.39	$909.35	$909.40